Planetary gear train of automatic transmission for vehicle

ABSTRACT

The present disclosure provides a planetary gear train of an automatic transmission for a vehicle including an input shaft, an output shaft, four planetary gear sets respectively having three rotational elements, and six control elements for selectively interconnecting the rotational elements and a transmission housing.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2016-0118081 filed on Sep. 13, 2016, which isincorporated herein by reference in its entirety.

FIELD

The present disclosure relates to a planetary gear train of an automatictransmission for a vehicle.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

In the field of an automatic transmission, more multiplicity ofshift-stages is used to enhance fuel efficiency and drivability of avehicle. The increase of oil price makes it difficult to improve fuelconsumption of a vehicle.

The engine downsizing has been attempted for purposes of weightreduction and fuel efficiency. Simultaneously, the development of moreshift stages of an automatic transmission has caused to provide theenhanced driving stability and fuel efficiency.

For more shift-stages of an automatic transmission, the number of partsis typically increased, which may affect installability, productioncost, weight and/or power flow efficiency.

In that aspect, less number of parts is desired to enhance fuelefficiency of an automatic transmission having more shift-stages.

An eight-speed automatic transmission has been introduced recently and aplanetary gear train for an automatic transmission enabling moreshift-stages is underdevelopment.

An automatic transmission of eight or more shift-stages typicallyincludes three to four planetary gear sets and five to seven controlelements (frictional elements), and this may largely affect the weightof the vehicle.

In this regard, disposing planetary gear sets in parallel or employingdog clutches instead of wet-type control elements has been attempted.However, such an arrangement may not be widely applicable, and using dogclutches may easily deteriorate shift-feel.

SUMMARY

The present disclosure provides a planetary gear train of an automatictransmission for a vehicle having shift-stages of ten forward speeds andone reverse speed by less number of parts, thereby improving powerdelivery performance and fuel consumption by multi-stages of anautomatic transmission, as well as driving stability of a vehicle byutilizing a low rotation speed of an engine.

A planetary gear train according to one form of the present disclosureincludes an input shaft configured to receive an engine torque; anoutput shaft configured to output a shifted torque; a first planetarygear set having a first, a second, and a third rotational elements; asecond planetary gear set having a fourth, a fifth, and a sixthrotational elements; a third planetary gear set having a seventh, aneighth, and a ninth rotational elements; a fourth planetary gear sethaving a tenth, an eleventh, and a twelfth rotational elements; a firstshaft connected to the first rotational element and the fourthrotational element; a second shaft connected to the second rotationalelement and the twelfth rotational element; a third shaft connected tothe third rotational element; a fourth shaft connected to the fifthrotational element and connected to the input shaft; a fifth shaftconnected with the sixth rotational element and the seventh rotationalelement, and selectively connected to the second shaft; a sixth shaftconnected to the eighth rotational element; a seventh shaft connected tothe ninth rotational element and the tenth rotational element, andselectively connected to the fourth shaft and the fifth shaftrespectively; and an eighth shaft connected to the eleventh rotationalelement, selectively connected to the sixth shaft, and connected to theoutput shaft.

The first shaft and the third shaft may be selectively connected to atransmission housing, respectively.

The first, the second, and the third rotational elements of the firstplanetary gear set may be respectively a first sun gear, a first planetcarrier, and a first ring gear of the first planetary gear set. Thefourth, the fifth, and the sixth rotational elements of the secondplanetary gear set may be respectively a second sun gear, a secondplanet carrier; and a second ring gear of the second planetary gear set.The seventh, the eighth, and the ninth rotational elements of the thirdplanetary gear set may be respectively a third sun gear, a third planetcarrier, and a third ring gear of the third planetary gear set. Thetenth, the eleventh, and the twelfth rotational elements of the fourthplanetary gear set may be respectively a fourth sun gear, a fourthplanet carrier, and a fourth ring gear of the fourth planetary gear set.

The first, the second, the third, and the fourth planetary gear sets maybe arranged in an order the first, the second, the third, and the fourthfrom an engine side.

A planetary gear train according to one form of the present disclosuremay further include a first clutch selectively connecting the fifthshaft and the seventh shaft; a second clutch selectively connecting thesixth shaft and the eighth shaft; a third clutch selectively connectingthe fourth shaft and the seventh shaft; a fourth clutch selectivelyconnecting the second shaft and the fifth shaft; a first brakeselectively connecting the first shaft and the transmission housing; anda second brake selectively connecting the third shaft and thetransmission housing.

A planetary gear train according to one form of the present disclosuremay realize at least ten forward speeds and at least one reverse speedby operating the four planetary gear sets and controlling six controlelements.

In addition, a planetary gear train according to one form of the presentdisclosure may improve driving stability when realizing shift-stagesbecome suitable for rotation speed of an engine.

Moreover, a planetary gear train according to one form of the presentdisclosure may increase engine driving efficiency by multi-stages of anautomatic transmission, and may further improve power deliveryperformance and fuel efficiency.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a planetary gear train; and

FIG. 2 is an operational chart for respective control elements atrespective shift-stages in a planetary gear train.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

In the following description, dividing names of components into first,second and the like is to avoid any confusion as the names of thecomponents are identical to one another; thus, an order thereof is notparticularly limited.

FIG. 1 is a schematic diagram of a planetary gear train according to oneform of the present disclosure.

Referring to FIG. 1, a planetary gear train according to one form of thepresent disclosure includes a first, a second, a third, and a fourthplanetary gear sets PG1, PG2, PG3, and PG4 arranged on a same axis,input shaft IS, output shaft OS, eight shafts TM1 to TM8 connected torotational elements of the first, the second, the third, and the fourthplanetary gear sets PG1, PG2, PG3, and PG4, control elements of fourclutches C1 to C4 and two brakes B1 and B2, and a transmission housingH.

Torque taken from the input shaft IS is shifted by cooperative operationof the first, the second, the third, and the fourth planetary gear setsPG1, PG2, PG3, and PG4, and then delivered through the output shaft OS.

The planetary gear sets are arranged in the order of the first, thesecond, the third, and the fourth from an engine side.

The input shaft IS is an input member and the torque from a crankshaftof an engine is delivered into the input shaft IS, after beingtorque-converted through a torque converter.

The output shaft OS is an output member, and being arranged on a sameaxis with the input shaft IS, delivers a shifted driving torque to adrive shaft through a differential apparatus (not shown).

The first planetary gear set PG1 is a single pinion planetary gear set,and includes a first sun gear S1, a first planet carrier PC1 thatrotatably supports a plurality of first pinion gears P1 externallygear-meshed with the first sun gear S1, and a first ring gear R1 that isinternally gear-meshed with the plurality of first pinion gears P1. Thefirst sun gear S1 acts as a first rotational element N1, the firstplanet carrier PC1 acts as a second rotational element N2, and the firstring gear R1 acts as a third rotational element N3.

The second planetary gear set PG2 is a single pinion planetary gear set,and includes a second sun gear S2, a second planet carrier PC2 thatrotatably supports a plurality of second pinion gears P2 externallygear-meshed with the second sun gear S2, and second ring gear R2 that isinternally gear-meshed with the plurality of second pinion gears P2. Thesecond sun gear S2 acts as a fourth rotational element N4, the secondplanet carrier PC2 acts as a fifth rotational element N5, and the secondring gear R2 acts as a sixth rotational element N6.

The third planetary gear set PG3 is a single pinion planetary gear set,and includes a third sun gear S3, a third planet carrier PC3 thatrotatably supports a plurality of third pinion gears P3 externallygear-meshed with the third sun gear S3, and a third ring gear R3 that isinternally gear-meshed with the plurality of third pinion gears P3. Thethird sun gear S3 acts as a seventh rotational element N7, the thirdplanet carrier PC3 acts as an eighth rotational element N8, and thethird ring gear R3 acts as a ninth rotational element N9.

The fourth planetary gear set PG4 is a single pinion planetary gear set,and includes a fourth sun gear 34, a fourth planet carrier PC4 thatrotatably supports a plurality of fourth pinion gears P4 externallygear-meshed with the fourth sun gear S4, and a fourth ring gear R4 thatis internally gear-meshed with the plurality of fourth pinion gears P4.The fourth sun gear S4 acts as a tenth rotational element N10, thefourth planet carrier PC4 acts as an eleventh rotational element N11,and the fourth ring gear R4 acts as a twelfth rotational element N12

In the arrangement of the first, second, third, and fourth planetarygear sets PG1, PG2, PG3, and PG4, the first rotational element N1 andthe fourth rotational element N4 are directly interconnected, the secondrotational element N2 and the twelfth rotational element N12 aredirectly interconnected, the sixth rotational element N6 and the seventhrotational element N7 are directly interconnected, and the ninthrotational element N9 and the tenth rotational element N10 are directlyinterconnected, respectively, by one of eight shafts TM1 to TM8.

The eight shafts TM1 to TM8 are arranged as follows.

Each of the eight shafts TM1 to TM8 may be a rotational member thatdirectly interconnects the input and output shafts and rotationalelements of the planetary gear sets PG1, PG2, PG3, and PG4, or may be arotational member that selectively interconnects a rotational element tothe transmission housing H, or may be a fixed member fixed to thetransmission housing H.

The first shaft TM1 is connected to the first rotational element N1(first sun gear S1) and the fourth rotational element N4 (second sungear S2), and selectively connected to the transmission housing H,thereby selectively acting as a fixed element.

The second shaft TM2 is connected to the second rotational element N2(first planet carrier PC1) and the twelfth rotational element N12(fourth ring gear R4).

The third shaft TM3 is connected to the third rotational element N3(first ring gear R1), and selectively connected to the transmissionhousing H, thereby selectively acting as a fixed element.

The fourth shaft TM4 is connected to the fifth rotational element N5(second planet carrier PC2), and directly connected to the input shaftIS, thereby always acting as an input element.

The fifth shaft TM5 is connected to the sixth rotational element N6(second ring gear R2) and the seventh rotational element N7 (third sungear S3), and selectively connected to the second shaft TM2.

The sixth shaft TM6 is connected to the eighth rotational element N8(third planet carrier PC3).

The seventh shaft TM7 is connected to the ninth rotational element N9(third ring gear R3) and the tenth rotational element N10 (fourth sungear S4), and selectively connected to the fourth shaft TM4 and thefifth shaft TM5 respectively.

The eighth shaft TM8 is connected to the eleventh rotational element N11(fourth planet carrier PC4), selectively connected to the sixth shaftTM6, and directly connected to the output shaft OS, thereby alwaysacting as an output element.

The eight shafts TM1 to TM8, the input shaft IS, and the output shaft OSmay be selectively interconnected to one another by control elements offour clutches C1, C2, C3, and C4.

The eight shafts TM1 to TM8 may be selectively connected to thetransmission housing H, by control elements of two brakes B1 and B2.

The four clutches C1 to C4 and the two brakes B1 and B2 are arranged asfollows.

The first clutch C1 is arranged between the fifth shaft TM5 and theseventh shaft TM7, and selectively connects the fifth shaft TM5 and theseventh shaft TM7, thereby controlling power delivery therebetween.

The second clutch C2 is arranged between the sixth shaft TM6 and theeighth shaft TM8, and selectively connects the sixth shaft TM6 and theeighth shaft TM8, thereby controlling power delivery therebetween.

The third clutch C3 is arranged between the fourth shaft TM4 and theseventh shaft TM7, and selectively connects the fourth shaft TM4 and theseventh shaft TM7, thereby controlling power delivery therebetween.

The fourth clutch C4 is arranged between the second shaft TM2 and thefifth shaft TM5, and selectively connects the second shaft TM2 and thefifth shaft TM5, thereby controlling power delivery therebetween.

The first brake B1 is arranged between the first shaft TM1 and thetransmission housing H, and selectively connects the first shaft TM1 tothe transmission housing H.

The second brake B2 is arranged between the third shaft TM3 and thetransmission housing H, and selectively connects the third shaft TM3 tothe transmission housing H.

The control elements of the first, the second, the third, and the fourthclutch C1, C2, C3, and C4 and the first and, the second brake B1, B2 maybe realized as multi-plate hydraulic pressure friction devices that arefrictionally engaged by hydraulic pressure.

FIG. 2 is an operational chart for respective control elements atrespective shift-stages in a planetary gear train according to one formof the present disclosure.

Referring to FIG. 2, a planetary gear train according to one form of thepresent disclosure realizes ten forward speeds and one reverse speed byoperating three control elements among the first, the second, the third,and the fourth clutches C1, C2, C3, and C4 and the first and the secondbrakes B1 and B2 at respective shift-stages.

In the forward first speed D1, the third clutch C3 and the first and thesecond brakes B1 and B2 are simultaneously operated.

As a result, the fourth shaft TM4 is connected to the seventh shaft TM7by the operation of the third clutch C3. In this state, the torque ofthe input shaft IS is delivered to the fourth shaft TM4 and the seventhshaft TM7.

In addition, the first shaft TM1, the third shaft TM3 acts as a fixedelement by the operation of the first and the second brakes B1 and B2,thereby realizing the forward first speed by cooperative operation ofrespective shafts and delivering a shifted torque to the output shaft OSconnected to the eighth shaft TM8.

In the forward second speed D2, the first clutch C1 and the first andthe second brakes B1 and B2 are simultaneously operated.

As a result, the fifth shaft TM5 is connected to the seventh shaft TM7by the operation of the first clutch C1. In this state, the torque ofthe input shaft IS is delivered to the fourth shaft TM4.

In addition, the first shaft TM1, the third shaft TM3 acts as a fixedelement by the operation of the first and the second brakes B1 and B2,thereby realizing the forward second speed by cooperative operation ofrespective shafts and delivering a shifted torque to the output shaft OSconnected to the eighth shaft TM8.

In the forward third speed D3, the first and the third clutches C1 andC3 and the second brake B2 are simultaneously operated.

As a result, the fifth shaft TM5 is connected to the seventh shaft TM7by the operation of the first clutch C1 and the fourth shaft TM4 isconnected to the seventh shaft TM7 by the operation of the third clutchC3. In this state, the torque of the input shaft IS is delivered to thefourth shaft TM4 and the seventh shaft TM7.

In addition, the third shaft TM3 acts as a fixed element by theoperation of the second brake B2, thereby realizing the forward thirdspeed by cooperative operation of respective shafts and delivering ashifted torque to the output shaft OS connected to the eighth shaft TM8.

In the forward fourth speed D4, the first and the fourth clutches C1 andC4 and the second brake B2 are simultaneously operated.

As a result, the fifth shaft TM5 is connected to the seventh shaft TM7by the operation of the first clutch C1, and the second shaft TM2 isconnected to the fifth shaft TM5 by the operation of the fourth clutchC4. In this state, the torque of the input shaft IS is delivered to thefourth shaft TM4.

In addition, the third shaft TM3 acts as a fixed element by theoperation of the second brake B2, thereby realizing the forward fourthspeed by cooperative operation of respective shafts and delivering ashifted torque to the output shaft OS connected to the eighth shaft TM8.

In the forward fifth speed D5, the third and the fourth clutches C3 andC4 and the second brake B2 are simultaneously operated.

As a result, the fourth shaft TM4 is connected to the seventh shaft TM7by the operation of the third clutch C3, and the second shaft TM2 isconnected to the fifth shaft TM5 by the operation of the fourth clutchC4. In this state, the torque of the input shaft IS is delivered to thefourth shaft TM4 and the seventh shaft TM7.

In addition, the third shaft TM3 acts as a fixed element by theoperation of the second brake B2, thereby realizing the forward fifthspeed by cooperative operation of respective shafts and delivering ashifted torque to the output shaft OS connected to the eighth shaft TM8.

In the forward sixth speed D6, the second and the third clutches C2 andC3 and the second brake B2 are simultaneously operated.

As a result, the sixth shaft TM6 is connected to the eighth shaft TM8 bythe operation of the second clutch C2, and the fourth shaft TM4 isconnected to the seventh shaft TM7 by the operation of the third clutchC3. In this state, the torque of the input shaft IS is delivered to thefourth shaft TM4 and the seventh shaft TM7.

In addition, the third shaft TM3 acts as a fixed element by theoperation of the second brake B2, thereby realizing the forward sixthspeed by cooperative operation of respective shafts and delivering ashifted torque to the output shaft OS connected to the eighth shaft TM8.

In the forward seventh speed D7, the first, the second, and the thirdclutches C1, C2, and C3 are simultaneously operated.

As a result, the fifth shaft TM5 is connected to the seventh shaft TM7by the operation of the first clutch C1, the sixth shaft TM6 isconnected to the eighth shaft TM8 by the operation of the second clutchC2, and the fourth shaft TM4 is connected to the seventh shaft TM7 bythe operation of the third clutch C3. In this state, the torque of theinput shaft IS is delivered to the fourth shaft TM4 and the seventhshaft TM7.

In this case, the first, the second, the third, and the fourth planetarygear sets PG1, PG2, PG3, and PG4 integrally rotate, and a torque isoutputted as inputted, thereby forming the forward seventh speed anddelivering a shifted torque to the output shaft OS connected to theeighth shaft TM8.

In the forward eighth speed D8, the second and the third clutches C2 andC3 and the first brake B1 are simultaneously operated.

As a result, the sixth shaft TM6 is connected to the eighth shaft TM8 bythe operation of the second clutch C2, and the fourth shaft TM4 isconnected to the seventh shaft TM7 by the operation of the third clutchC3. In this state, the torque of the input shaft IS is delivered to thefourth shaft TM4 and the seventh shaft TM7.

In addition, the first shaft TM1 acts as a fixed element by theoperation of the first brake B1, thereby realizing the forward eighthspeed, which is an overdrive gear, by cooperative operation ofrespective shafts and delivering a shifted torque to the output shaft OSconnected to the eighth shaft TM8.

In the forward ninth speed D9, the third and the fourth clutches C3 andC4 and the first brake B1 are simultaneously operated.

As a result, the fourth shaft TM4 is connected to the seventh shaft TM7by the operation of the third clutch C3, and the second shaft TM2 isconnected to the fifth shaft TM5 by the operation of the fourth clutchC4. In this state, the torque of the input shaft IS is delivered to thefourth shaft TM4 and the seventh shaft TM7.

In addition, the first shaft TM1 acts as a fixed element by theoperation of the first brake B1, thereby realizing the forward ninthspeed, which is an overdrive gear, by cooperative operation ofrespective shafts and delivering a shifted torque to the output shaft OSconnected to the eighth shaft TM8.

In the forward tenth speed D10, the second and the fourth clutches C2and C4 and the first brake B1 are simultaneously operated.

As a result, the sixth shaft TM6 is connected to the eighth shaft TM8 bythe operation of the second clutch C2, and the second shaft TM2 isconnected to the fifth shaft TM5 by the operation of the fourth clutchC4. In this state, the torque of the input shaft IS is delivered to thefourth shaft TM4.

In addition, the first shaft TM1 acts as a fixed element by theoperation of the first brake B1, thereby realizing the forward tenthspeed, which is a highest gear, by cooperative operation of respectiveshafts and delivering a shifted torque to the output shaft OS connectedto the eighth shaft TM8.

In the reverse speed REV, the second clutch C2 and the first and thesecond brakes B1 and B2 are simultaneously operated.

As a result, the sixth shaft TM6 is connected to the eighth shaft TM8 bythe operation of the second clutch C2. In this state, the torque of theinput shaft IS is delivered to the fourth shaft TM4.

In addition, the first shaft TM1 and the third shaft TM3 respectivelyact as fixed elements by the operation of the first and the secondbrakes B1 and B2, thereby realizing the reverse speed by cooperativeoperation of respective shafts and delivering a shifted torque to theoutput shaft OS connected to the eighth shaft TM8.

As described above, a planetary gear train according to one form of thepresent disclosure may realize the forward tenth speed and one reversespeed by operating four planetary gear set PG1, PG2, PG3, and PG4 bycontrolling four clutches C1, C2, C3, and C4 and two brakes B1 and B2.

In addition, a planetary gear train according to one form of the presentdisclosure may improve driving stability when shift-stages becomesuitable for rotation speed of an engine.

Moreover, a planetary gear train according to one form of the presentdisclosure may increase engine driving efficiency by multi-stages of anautomatic transmission, and may further improve power deliveryperformance and fuel efficiency.

The description of the disclosure is merely exemplary in nature and,thus, variations that do not depart from the substance of the disclosureare intended to be within the scope of the disclosure. Such variationsare not to be regarded as a departure from the spirit and scope of thedisclosure.

What is claimed is:
 1. A planetary gear train of an automatictransmission for a vehicle, comprising: an input shaft configured toreceive an engine torque; an output shaft configured to output a shiftedtorque; a first planetary gear set having a first, a second, and a thirdrotational elements; a second planetary gear set having a fourth, afifth, and a sixth rotational elements; a third planetary gear sethaving a seventh, an eighth, and a ninth rotational elements; a fourthplanetary gear set having a tenth, an eleventh, and a twelfth rotationalelements; a first shaft fixedly connected to the first rotationalelement and the fourth rotational element; a second shaft fixedlyconnected to the second rotational element and the twelfth rotationalelement; a third shaft fixedly connected to the third rotationalelement; a fourth shaft fixedly connected to the fifth rotationalelement and connected to the input shaft; a fifth shaft fixedlyconnected to the sixth rotational element and the seventh rotationalelement, and selectively connected to the second shaft; a sixth shaftfixedly connected to the eighth rotational element; a seventh shaftfixedly connected to the ninth rotational element and the tenthrotational element, and selectively connected to the fourth shaft andthe fifth shaft respectively; and an eighth shaft fixedly connected tothe eleventh rotational element, selectively connected to the sixthshaft, and connected to the output shaft.
 2. The planetary gear train ofclaim 1, wherein the first shaft and the third shaft are selectivelyconnected to a transmission housing respectively.
 3. The planetary geartrain of claim 2, further comprising: a first clutch selectivelyconnecting the fifth shaft and the seventh shaft; a second clutchselectively connecting the sixth shaft and the eighth shaft; a thirdclutch selectively connecting the fourth shaft and the seventh shaft; afourth clutch selectively connecting the second shaft and the fifthshaft; a first brake selectively connecting the first shaft and thetransmission housing; and a second brake selectively connecting thethird shaft and the transmission housing.
 4. The planetary gear train ofclaim 1, wherein: the first, the second, and the third rotationalelements of the first planetary gear set are respectively a first sungear, a first planet carrier, and a first ring gear of the firstplanetary gear set; the fourth, the fifth, and the sixth rotationalelements of the second planetary gear set are respectively a second sungear, a second planet carrier, and a second ring gear of the secondplanetary gear set; the seventh, the eighth, and the ninth rotationalelements of the third planetary gear set are respectively a third sungear, a third planet carrier, and a third ring gear of the thirdplanetary gear set; and the tenth, the eleventh, and the twelfthrotational elements of the fourth planetary gear set are respectively afourth sun gear, a fourth planet carrier, and a fourth ring gear of thefourth planetary gear set.
 5. The planetary gear train of claim 1,wherein the first, the second, the third, and the fourth planetary gearsets are arranged in an order of the first, the second, the third, andthe fourth from an engine side.
 6. A planetary gear train of anautomatic transmission for a vehicle, comprising: an input shaftconfigured to receive an engine torque; an output shaft configured tooutput a shifted torque; a first planetary gear set having a first, asecond, and a third rotational elements; a second planetary gear sethaving a fourth, a fifth, and a sixth rotational elements; a thirdplanetary gear set having a seventh, an eighth, and a ninth rotationalelements; and a fourth planetary gear set having a tenth, an eleventh,and a twelfth rotational elements, wherein the input shaft is connectedto the fifth rotational element, the output shaft is connected to theeleventh rotational element, the first rotational element is fixedlyconnected to the fourth rotational element, the second rotationalelement is fixedly connected to the twelfth rotational element, thesixth rotational element is fixedly connected to the seventh rotationalelement, the ninth rotational element is fixedly connected to the tenthrotational element, the second rotational element is selectivelyconnected to the sixth rotational element, the eighth rotational elementis selectively connected to the eleventh rotational element, and thetenth rotational element is selectively connected to the fifth and theseventh rotational element respectively.
 7. The planetary gear train ofclaim 6, wherein the first rotational element and the third rotationalelement are selectively connected to the transmission housing,respectively.
 8. The planetary gear train of claim 7, furthercomprising: a first clutch selectively connecting the seventh rotationalelement and the tenth rotational element; a second clutch selectivelyconnecting the eighth rotational element and the eleventh rotationalelement; a third clutch selectively connecting the fifth rotationalelement and the tenth rotational element; a fourth clutch selectivelyconnecting the second rotational element and the sixth rotationalelement; a first brake selectively connecting the first rotationalelement and the transmission housing; and a second brake selectivelyconnecting the third rotational element and the transmission housing. 9.The planetary gear train of claim 6, wherein: the first, the second, andthe third rotational elements of the first planetary gear set arerespectively a first sun gear, a first planet carrier, and a first ringgear of the first planetary gear set; the fourth, the fifth, and thesixth rotational elements of the second planetary gear set arerespectively a second sun gear, a second planet carrier, and a secondring gear of the second planetary gear set; the seventh, the eighth, andthe ninth rotational elements of the third planetary gear set arerespectively a third sun gear, a third planet carrier, and a third ringgear of the third planetary gear set; and the tenth, the eleventh, andthe twelfth rotational elements of the fourth planetary gear set arerespectively a fourth sun gear, a fourth planet carrier, and a fourthring gear of the fourth planetary gear set.
 10. The planetary gear trainof claim 6, wherein the first, the second, the third, and the fourthplanetary gear sets are arranged in an order of the first, the second,the third, and the fourth from an engine side.